The present invention relates to a process for converting mixed waste plastic (MWP) into valuable petrochemicals. More in detail, the present process comprises feeding mixed waste plastic (MWP) to a pyrolysis reactor, converting said MWP into a gaseous stream and a liquid stream, and further processing said gaseous stream into valuable petrochemicals.
WO2013/169367 relates to a process for making a high VI lubricating base oil, comprising: a) hydrocracking a blend, comprising (1) a heavy wax derived from pyrolyzing a plastic feed and (2) a lube oil feedstock, in a lube hydrocracking zone in the presence of a hydrocracking catalyst and hydrogen under lube hydrocracking conditions to produce a hydrocracked stream; and b) dewaxing at least a portion of the hydrocracked stream in a hydroisomerization zone in the presence of a hydroisomerization catalyst and hydrogen under hydroisomerization conditions to produce a base oil. Heavy waxes can be prepared by pyrolyzing a plastic feed by means well known to those of skill in the art and are described, for example, in U.S. Pat. No. 6,143,940. The pyrolysis zone effluent typically contains a broad boiling point range of materials. The pyrolysis zone effluent (liquid portion) is very waxy and has a high pour point. It comprises n-paraffins and some olefins.
WO2013/169367 thus discloses a process for producing high VI lube base oils by a process of hydrocracking followed by hydroisomerization and hydrofinishing and employs as feed a mixture of heavy wax from pyrolysis of plastics and a conventional lube oil feedstock. The heavy wax contains 30-90 wt % n-paraffins, 5-25 wt % olefins and <5 wt % aromatics. WO2013/169367 teaches that by co-feeding heavy wax in a hydrocracker feed, the heavy wax concentrated in the 343+ deg C. cut of the product. The objective of this reference is to maximize the 343+ deg C. cut of the products, i.e. to maximize lube base oils (343+ deg C.).
US patent application No 2009/151233 relates to a method comprising the steps of: a) pyrolyzing biomass concurrently with a waste plastic, wherein said waste plastic comprises at least about 75 wt. % polyolefins at a temperature of from about 450° C. to about 650° C. so as to yield pyrolysis oil; b) separating the pyrolysis oil into at least two component fractions comprising a 650° F.−fraction and a 650° F.+fraction; c) hydrotreating at least one of the at least two component fractions so as to yield at least one hydrotreated intermediate; and d) catalytically-isomerizing the at least one hydrotreated intermediate so as to yield at least one isomerized product. An object of US patent application No 2009/151233 is to maximize transportation fuels generated following the steps of co-feeding biomass and plastics to a pyrolysis unit, hydrotreating and isomerizing at least one boiling cut fraction in the product from pyrolysis unit to form a transportation fuel. US patent application No 2009/151233 is not concerned about co-feeding pyrolysis liquid along with petroleum feed to a hydrocracker and the stability of asphaltenes in the combined hydrocracker feed.
An article “Continuous upgrading of a plastics pyrolysis liquid to an environmentally favorable gasoline range product”, H. S Joo et al, Fuel Processing Technology, 1 Jan. 1998 (1998-01-01), pages 25-40 relates about upgrading a residual liquid from plastics pyrolysis to a gasoline range product using a three-step sequential process consisting of hydrotreating, hydrocracking and distillation, wherein the original as-received pyrolysis liquid was separated into two fractions by distillation at 90° C. and 20 millibar, and the feed material was the residual fraction amounting to 58% of the raw plastics pyrolysis liquid. This residual fraction was an opaque black liquid containing 71 wt. % gas oil fraction (+205° C.) and 29 wt. % naphtha fraction according to the boiling point distribution. This reference is concerned with hydrocracking of a residual liquid from a plastic pyrolysis process. The liquid products from the pyrolysis process is distilled to produce a distillate fraction (48 wt %) and a residual liquid fraction (52 wt %). This residual liquid fraction containing 29 wt % naphtha range hydrocarbons and 71 wt % hydrocarbons boiling above 205 deg C. is the feed to the hydrocracking process. The product contained 46 wt % of material in the gasoline boiling range. This reference does not thus teach an integrated process for maximizing petrochemicals.
JP11061147A and JP11061148A disclose a method of the pyrolysis of plastics wherein pyrolysis oil is hydrogenated to free it from chlorine and mixed with petroleum oil and fed to a refining unit.
JP10310778A discloses a process wherein pyrolysis oil at 0-100 vol % is mixed with a petroleum stream boiling below 250° C. and fed to a FCC unit. The pyrolysis oil quality should have 0.1-5 g dienes/100 g, 0.0007-1 wt % chlorine and 0.0001-1 wt % oxygen.
Waste plastics are mostly diverted to landfills or are incinerated, with a smaller fraction being diverted to recycling. Over the years, with increased regulations and levies on landfills, the percentage of the post-consumer waste being recycled or incinerated for energy recovery is gradually increasing. The 2009 statistics by Plastics Europe indicate that approximately 24.4 million tons of waste plastics were generated in Europe. Of this, 54% was treated either through recycling (22.6%) or energy recovery (31.3%). Plastics diverted to landfills were approximately 46.1%. Thus, waste plastics disposal into landfills is becoming increasingly difficult.
Pyrolysis of waste plastics to products like naphtha, ethylene, propylene and aromatics can be classified under the category of feedstock recycling of waste plastics. With the naphtha prices increasing dramatically, steam crackers operating on naphtha feed are at a disadvantageous position compared to steam crackers operating on cheaper gaseous hydrocarbon feeds. If a portion of the naphtha feed to the steam crackers is replaced by an equivalent amount of products from plastics conversion processes, like pyrolysis, the economic situation for the steam crackers operating on naphtha feed will improve.
In order to make an impact on the economics of very large volumes in continuous steam cracker plant operations, it is necessary that the pyrolysis process is also continuous. No large scale plants exist today that directly convert waste plastics in a single step to petrochemicals. Previous attempts around the world have been focused on generation of liquid fuels from waste plastics. These plants were small in scale or modular in nature. Reactions carried out in such small scale plants are also carried out for longer residence times, making them less suitable for continuous operations on larger scales. Some earlier attempts have also focused at generating feedstocks for steam crackers from waste plastics. These rely on the availability of steam cracker furnaces for being successful, however. Furthermore, conversion of these produced steam cracker feeds in cracker furnaces would typically result in production of high amounts of methane, which is undesirable.
Pyrolysis of mixed plastic waste (MPW) provides yields of gases and liquids. The gaseous product yield is rich in olefinic components. The liquid product is rich in aromatics. Depending on the severity of operations in the pyrolysis reactor, the yields of light olefins from the pyrolysis reactor can be increased and the yield of aromatics can be increased. The liquid pyrolysis product has all classes of compounds in it in varying proportions i.e. paraffins, iso-paraffins, naphthenes, olefins and aromatics.